The present invention relates to a method for developing a resist film, more specifically to a dry development method for generating a desired pattern of a resist film on a substrate.
In the manufacturing of a semiconductor circuit, a wet process is generally employed for the development of a resist film formed on a substrate such as a silicon wafer. For instance, chloro-methyl polystyrene (CMS), which is widely used as a high resolution and high contrast negative type resist for electron beam lithography, is developed by an organic solution composed of iso-amyl acetate and ethyl cellosolve or of acetone and iso-propyl alcohol.
However, the wet development process for resist films usually involves the following problems: precise controls are required for the temperature and concentration of the developing solution (developer); and contamination of the substrate can occur from a residue mainly consisting of the removed resist which is dissolved in the developer or in the rinsing solution.
Negative type resist films generally have another problem relating to the tendency of swelling thereof when soaked in developing solutions such as an organic solution. The swelling is apt to leave a scum at the edge of the remaining resist film which results in the low resolution of the resist pattern as compared with the resolution achieved by using positive type resist films.
The above mentioned problems in the wet development also apply to the conventional photoresists, more or less, however, they are more serious for the resist films used in the electron beam lithography which is becoming indispensable to the modern VLSI trend requiring patterns of submicron dimensions.
The above problems in the wet development of resist films can be eliminated if a dry method is made practical for the development of resist films. Although several dry processes have been incorporated in the manufacturing of VLSI semiconductor circuits, it seems that there are only a few disclosures concerning dry development of resist films, including one utilizing an oxygen plasma for developing a negative photo-resist film. (J. N. Smith et al. "A Production Viable Plasma Developable Photoresist" Semiconductor International, December 1979.)
However, the above described dry development requires expensive equipment for producing the plasma, including a vacuum chamber and pumping system, a gas-introducing system for oxygen and a radio-frequency power supply system. Further, these systems require complicated and time consuming steps for controlling the process. Therefore, it is desired to provided a cost-effective dry development method that can be carried out in atmospheric air without involving any complicated process control. Further, the dry development method must be applicable to an electron beam resist.